March 2002 Newsletter

Stockton Astronomical Society

Valley Skies

Valley Skies - March 2002 Issue

Constellations:
Gemini the Twins

Gen: Geminorum
Abb: Gem
Dec: +10.0° to +35.4°
RA: 5 h 57m to 8h 6m

Gemini is one of the few constellations that looks like the object for which it is named, two people. For most of the mid-northern latitudes Gemini reaches its highest point in the sky around 10:00 P.M. on February 1^st. You can pick it out by looking for the two bright stars located 4.5° apart. The stars Castor (Alpha Gem) on the right and Pollux (Beta Gem) on the left, are the heads of the twins. The rest of Gemini’s stars can be seen running from each head in the northeast, to the feet, just in the Milky Way to the southwest.

According to Greek and Roman mythology, the twins Castor and Pollux were the sons of Leda, the woman that Zeus seduced in the guise of a swan. In some versions of the story only Pollux was the son of the god; Castor’s father was Leda’s mortal husband. Castor was known most as a horse trainer, and Pollux was a great boxer. They participated in many heroic quests, not the least of which was with Jason in search of the Golden Fleece.

The twins love for each other was legendary. When Castor was killed in a fight, Pollux begged Zeus to let him die too. Zeus was so moved by Pollux’s devotion to his brother, that he let Castor take Pollux’s place among the living every other day for the remainder of Pollux’s life. After Pollux’s death Zeus placed them together in the sky.

Exploring the Twins

There are many multiple systems in Gemini, starting with Castor (a Gem), which is made up of six stars. In a moderate telescope you can see two bright stars and a fainter third star; each of these is a binary star. The total light from these stars shines at magnitude 1.6, making Castor one of the brightest "stars" in the sky.

From Castor look toward Pollux (b Gem). With these as the heads of the twins, imagine a triangle that would point to their shoulders: this point is the approximate location of NGC 2371 and 2372. NGC 2371&2 is a planetary nebula that appears as a figure 8, being two lobes straddling the central star.

Off the right arm of Pollux, hop about 2° east-southeast to NGC 2392, a great planetary nebula. In larger scopes this nebula takes on the appearance that earned it the name "Eskimo Nebula". The nebula is nearly pole-on to us; in large telescopes it looks like a face ringed by a fur hood. In smaller scopes it is a small, bluish green oval. Move a little over 2° to the east of the Eskimo Nebula and you will find NGC 2420. This is an open cluster with about 30 stars visible.

Return to Castor and follow the line of stars towards the southwest to eta (e) Gem. Eta marks the foot of Castor and will be the starting point for our final hop this month. From eta hop 2¼° northwest to NGC 2168 (M35). This is a spectacular open cluster, with a lot of stars brighter than 10^th magnitude near the center. Using a low power eyepiece, you will notice another hazy patch off to the side of M35. This is NGC 2158 a fainter but still easy to locate open cluster.

Gemini has a lot of binary and multiple star systems along with a couple of other planetary nebulas, so check your charts -- and happy hunting.

Clear Skies...Eric